The primary bottlenecks to the production of hydrocarbons from a well is the inflow rate from the hydrocarbon formation into the wellbore. The inflow is affected by near wellbore condition and formation characteristics. The near wellbore conditions and the formations of damaged wells can be positively influenced, with increased hydrocarbon production, through stimulation treatment. Methods for well stimulation include, but are not limited to, treatments with various chemicals, hydraulic fracturing where liquids are injected under high pressure (usually with propping agents), methods in which explosives are detonated within the formations to effect mechanical fracture, and combinations of the above procedures.
Oil and gas wells are subject to many ailments, some of which are treatable. One such ailment is a blockage of perforations resulting in dramatic or catastrophic decline in production. Some formations, such as an unconsolidated formation contain fines, such as sand, which flow into the perforation and become trapped, creating a plug or blockage in the perforation. Other examples of blockages, or bridging, are perforation debris, clays, silts, asphaltenes, drilling damage, and foreign or manmade objects. It is therefore desirable to remove these blockages from the perforations.
One such method is described in U.S. Pat. No. 4,617,997 to Jennings, Jr. which teaches a method to create or enhance fractures in a formation and extending these fractures with foam generated downhole. A foaming agent is mixed with an aqueous fluid and placed into the wellbore fluid, the level of the wellbore fluid being above the perforations and productive interval of the formation. A propellant housed in a canister, which is attached to a retrievable wire line, is placed next to the fractures. The propellant is ignited creating heat, gas and pressure while simultaneously initiating the formation of foam. The foam enters the fractures under such increased pressure for extending the radial fractures. When the pressure decreases and the foam collapses, the decreased viscosity of the wellbore fluid causes any resultant fluid and debris which has accumulated in the fractures to return into the wellbore. It is not disclosed if or how resulting accumulated and recovered debris is removed from the wellbore.
Another method is taught by Mohaupt in U.S. Pat. No. 6,138,753. Mohaupt teaches a technique for treating hydrocarbon wells, using two separate propellant ignition phases. A gas generator comprising a propellant charge, housed in a carrier having many openings, is lowered into the well in-line with the perforated interval. The gas generator is ignited and produces sufficient energy to breakdown and clean-out all of the perforations and create micro-fractures originating from the perforations. This is followed by igniting a second gas generator to inject a treatment liquid into the formation with energy less than that required to fracture the formation. No removal of resulting debris is contemplated.
A technique to both remove blockage mechanisms, debris and fines from perforations and to ensure the complete removal of this debris from the wellbore is needed. Although blockage removal from perforations or fractures is a by-product of some fracturing procedures, the method and results vary. Jennings Jr. uses the foam primarily for a different purpose, to extend the fractures and is limited to the amount of foam produced by the foaming agent. Mohaupt breaks down debris and cleans-out perforations but does not remove the debris from the well. Mohaupt also does not use foaming techniques. If blockage debris and fines are not completely removed from the wellbore, the remaining debris can re-block perforations, erode production equipment and seals, or plug the outside or the inside of the production tubing reducing or totally restricting production. Well clean-out procedures would be repeatedly required at a large expense.